update CI actions/checkout

Author: nitely

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
         # xxx trim to on use latest in each branch eg 1.0.10, 1.2.8 etc
         nim: [1.0.0, 1.0.2, 1.0.4, 1.0.10, 1.2.0, 1.2.2, 1.2.4, 1.2.6, 1.2.12, 1.4.0, 1.4.2, 1.4.8, 1.6.14, 2.0.0]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3.5.3
     - name: Run Tests
       run: |
         docker pull nimlang/nim:${{ matrix.nim }}